Roller Finger Followers (RFF) are widely used in overhead cam internal combustion engines to sequentially open and close the cylinder intake and exhaust valves. In a typical application, the RFF serves to transfer and translate rotary motion of a cam shaft lobe into a pivotal motion of the RFF to thereby open and close an associated valve.
It is known that, for a portion of the duty cycle of a typical multiple-cylinder engine, the performance load can be met by a functionally smaller engine having fewer firing cylinders, and that at low-demand times fuel efficiency can be improved if one or more cylinders of a larger engine can be withdrawn from firing service. It is also known that at times of low torque demand, valves may be opened to only a low lift position to conserve fuel, and that at times of high torque demand, the valves may be opened wider to a high lift position to admit more fuel. It is known in the art to accomplish this by de-activating a portion of the valve train or limiting the opening of one or more valves associated with pre-selected cylinders in any of various ways. One way is by providing a special two-step RFF having a variably latchable and de-latchable central slider arm which may be positioned for contact with a high lift lobe of the cam shaft. Such a two-step RFF typically is also configured with rollers disposed at each side of the slider arm for contact with low lift lobes of the cam shaft on either side of the high-lift lobe. Thus, the two-step RFF causes low lift of the associated valve when the slider arm of the RFF is in a de-latched or deactivated position, and high lift of the associated valve when the slider arm of the RFF is latched in an activated position to engage the high lift lobe of the cam shaft.
One such two-step RFF known in the art comprises a generally elongate body having a pallet end in contact with an axially movable valve stem and an opposing socket end in contact with a stationary pivot such as, for example, a hydraulic lash adjuster (HLA). A moveable and therefore deactivatable high lift slider is positioned central to the RFF body. Rollers are rotatably mounted on each side of the slider on a non-rotatable shaft fixed to the body. The rollers ride on narrow bearings, as for example needle bearings. End washers are used to rotatably fix the rollers and bearings to the shaft and to restrain the rollers and bearings from moving laterally on the shaft.
The width of the bearings in this prior art follower is limited to the width of the rollers themselves. Further, because the bearings are disposed outside the body side walls, the bearings are substantially shielded from flow of lubricating oil within the RFF body.
Another prior art two-step roller finger follower is disclosed in U.S. Pat. No. 6,755,167 B2, issued Jun. 29, 2004, the relevant disclosure of which is incorporated herein by reference. In this roller finger follower, an elongate body having first and second side members defines coaxially disposed shaft orifices. A pallet end and a socket end interconnect with the first and second side members to define a central slider arm aperture and a latch pin channel. The socket end is adapted to mate with a mounting element such as an hydraulic lash adjuster, and the pallet end is adapted to mate with a valve stem, pintle, lifter, or the like. A slider arm for engaging a high-lift cam lobe is disposed in the slider arm aperture and has first and second ends, the first end of the slider arm being pivotally mounted to one end of the body and the second end defining a slider tip for engaging an activation/deactivation latch. The latch pin is slidably disposed in the latch pin channel, the latch pin having a nose section for selectively engaging the slider tip. A spool-shaped roller comprising a shaft and opposed roller elements fixedly attached to ends of the shaft is rotatably disposed in the shaft orifices, the roller being adapted to follow the surface motion of a low-lift cam lobes. Preferably, the shaft is journalled in roller or needle bearings which extend between and through both the first and second shaft orifices, being thus exposed to normal copious oil flow through central regions of the RFF.
A drawback of this prior art roller finger follower is that the axis of the locking pin intersects the axis of the pivot pin for the slider; i.e., the motion of the locking pin is along an extension of a pivot pin and slider tip radius. Thus, the motion of the slider tip is substantially orthogonal to the path of the locking pin. This relationship necessitates that the locking pin extend from its supporting bore in order to engage the slider tip, thereby engendering a bending moment on the locking pin. Providing acceptable support for such bending moment requires that the locking pin have a relatively long bore and large diameter, thus increasing undesirably the size of the follower body and hence the overall follower assembly.
A further drawback of such a roller finger follower is that the locking pin can inadvertently engage the wrong side of the slider tip if the locking pin is commanded to move when the slider is fully depressed by the cam lobe, causing the follower to become locked in the full lost-motion position, which condition is highly undesirable.
It is a principal object of the present invention to eliminate the bending moment inherent in the prior art follower.
It is also an object of the invention to prevent inadvertent locking of a follower in the full lost-motion position.